Sunday, January 17, 2010
10:10 PM | Posted by Sweep Commander | Edit Post
While summer nesting season on Alcatraz is a bonanza for bird nerds, here is one reason why winter season can be just as rewarding for those tickled by bird life and behavior.
On November 22, 2009, fellow Maganrord blogger BourbonHawk, National Park Service Ranger John Cantwell and I got our first glimpse of the peregrine falcon now making itself at home in the tops of the island's cypress and eucalyptus trees, the water tower, the top of the power plant's smoke stack, and the shoots of agave adjacent to the west road and parade ground. A careful survey of these areas will give you a better than even chance of spotting it.
This peregrine is about the size of a seagull or a raven and is thus a probable female, though this is a difficult determination to make. Male and female falcons display what wildlife biologists like to call "reverse sexual dimorphism" – a term that is so ill conceived I'm embarrassed to even use it. In the zoology biz it means that males of the species are generally smaller than females. Regular old "sexual dimorphism" is present in species where males are larger. (C'mon, wildlife biologists. This is silly. Having smaller males than females is just the other kind of sexual dimorphism. Don't make me tell you your business!)
She is a formidable and sharply observant hunter. When a peckish peregrine notices a small or medium sized bird flying below, her wings fold in and the barrel of her body tips down towards the earth as she begins to dive. A peregrine dive was once clocked at 242 miles per hour, the fastest known speed to be reached by any animal under its own power. For the falcon, a successful dive yields an instantaneous kill.
It's a good bet that she's taken a few pigeons and starlings off our hands.
Worldwide, the peregrine lives and breeds on six continents and has around 20 recognized subspecies. Our falcon is a probably a member of the North American variety, Falco peregrinus anatum. 'Anatum', being latin for "duck eater", references the the bird's love of duck meat. For the same reason, the North American peregrine was once also known as the duck hawk.
Even given its record setting aeronautical feats, what's remarkable about this falcon is its survival story. The first half of the 20th century was as gloomy for the peregine as it was on Alcatraz. Though a fearsome bird, anatum proved defenseless against the scourge of the pesticide DDT. Widely used in American agriculture from the 1940s through its eventual ban in 1972, DDT's effects upon birds were as brOOtal as any metal front man's growl. The pesticide thinned anatum's eggshells and the embryos enclosed in these defective confines failed in catastrophic numbers. The peregrine falcon almost disappeared from the North American continent, and the anatum subspecies nearly disappeared from the planet.
We owe the pleasure of our falcon's visit, at least in part, to a popular movement that raised awareness of the public health and environmental dangers of DDT and eventually secured a ban on the agricultural use of the toxin. A captive breeding program for peregrine falcons was then instrumental in resuscitating the North American population. The species has even been successful in adapting to city life, very much enjoying the taste of our urban pigeon populations.
We here at Maganrord HQ would argue that not only is our visiting peregrine undeniably rad, but that whenever a member of a recovering bird population – poisoned by human activity to the threshold of extinction – can find a winter home in a fortress prison turned National Park site and bird sanctuary, she is a living reminder of the powerful impact made by our popular conservation movements.
Sadly, it's not all unicorns and rainbows for the brave heroine. Her stay with us is likely to be relatively brief given her uneasy rapport with the island's year-round inhabitants. We've seen her struggle violently in mid-air with the island's raven pair. She's also made aggressive gestures towards our seagulls who've retaliated by collectively chasing her into the bay, though so far, she has always returned. With breeding season and fledgeling chicks to protect on the horizon, we amateurs at Maganrord expect the island's gull population to turn up the heat on the wintering falcon if she doesn't decide to leave on her own terms.
Still, it's pretty good while it lasts.
- ▼ 2010 (73)